Various arrangements are known in the prior art for providing a illuminator for a film scanner. One such conventional illuminator is a basic linear integrating cavity which is disclosed in U.S. Pat. No. 4,868,383 (A. Kurtz et al.), issued on Sept. 19, 1989. A basic integrating cylinder has a cylindrical cavity comprising an interior white diffusing surface of high reflectivity, a light entry port, and a light exiting slit. Light from an external source is input into the cylindrical cavity (e.g., at the top or bottom) via an optical system of relay and condensing lenses. The light entry port for the light from the external source is located ninety degrees from the light exiting slit of the cavity. The light scatters throughout the cavity, and exits through the slit (e.g., at the front) to provide diffuse uniform DeJager et al.), issued on Apr. 30, 1991, discloses an illumination system using the conventional linear integrating cavity in a telecine film scanner.
To accomplish the illumination of the film, the integrating cavity must be incorporated into a film gate mechanism. Such film gate, as used in the film scanner shown in FIG. 1 of U.S. Pat. No. 4,868,383, or the telecine film scanner shown in FIG. 1 of U.S. Pat. No. 5,012,346, includes the integrating cavity, the input optical system comprising a complex arrangement of many elements (condensing and relay lenses, mirrors, and filters) for directing the light beam into the integrating cavity, a skid surface on which the film rides, a feedback path from the integrating cavity to a light source, and various film guiding mechanisms to provide film steadiness and registration. Such film gate is a complicated assembly wherein various components are competing for the same space. Therefore, the mechanical design of the film gate involves a careful tradeoff of these conflicting interests.
In FIG. 9 of U.S. Pat. No. 4,868,383 (discussed hereinbefore), there is shown a general concept of an end input illuminated integrating cavity which relieves some of the problem of various components of a film gate competing for the same space. The integrating cavity of FIG. 9 introduces multiple light beams through the opposing ends of the cavity to improve uniformity of the diffuse light at the output slit when the integrating cylinder is in excess of 75 millimeters in length.
In general, a well-optimized end input illuminated integrating cylinder can provide a more uniform diffuse light across the output slit than the conventional integrating cavity shown in FIGS. 1 and 2 of U.S. Pat. No. 4,868,383. However, such end input illuminated integrating cylinder is more complex and requires a knowledge of what is required to optimize such end input illuminated integrating cylinder in order to provide the more uniform diffuse light across the output slit. This patent, however, does not provide an explanation of what is required to set up the various components (e.g., input port to exit slit relationship, light beam configuration, cavity size, etc.) in order to optimize an end input illuminated integrating cylinder.
U.S. Pat. No. 5,103,385 (R. Federico et al.), issued on Apr. 7, 1992, discloses a linear light source arrangement for a film scanner illustrating a second type of illuminator known in the prior art. The linear light source comprises an elongated light integrating cavity having diffusely reflective walls. Light is introduced into the cavity through an input port, and an output beam of diffuse illumination is produced through an output slit parallel to a longitudinal axis of the integrating cavity and opposite (180 degrees) the input port. A baffle is disposed in the cavity parallel to the longitudinal axis to prevent light from passing directly from the input port to the output slit. The surfaces of the integrating cavity walls adjacent the output slit are generally planar and are disposed at an angle to an optical axis of the diffuse output beam.
The linear light source arrangement of U.S. Pat. No. 5,103,385 advantageously shifts the input optics further from a surface on which the film rides. This provides a technique for alleviating the spacing conflicts found with the film gate used in film scanners as indicated hereinabove. However, a baffle is required to avoid the light from exiting the exit slit with a nonuniform distribution. When comparing such integrating cavity arrangement (input port opposite the exit slit) with that of the conventional integrating cavity arrangement (input port at 90 degrees to the exit slit), the former integrating cavity arrangement (of U.S. Pat. No. 5,103,385) is found to be less efficient than the conventional integrating cavity arrangement, and, therefore, may not always be used.
U.S. Pat. No. 4,899,040 (M. Davis et al.), issued on Feb. 6, 1990, and U.S. Pat. No. 4,933,779 (J. Milch), issued on Jun. 12, 1990, disclose an illumination system for an image scanner comprising a bundle of optical fibers and a tube. A beam of light from the light source is intercepted by the bundle of optical fibers which are then unbundled to provide a line of illumination. The tube has a reflective inner surface and defines a light input slit disposed parallel to a longitudinal axis of the tube for receiving the line of illumination from the unbundled optical fibers, and a diffuse light output slit disposed parallel to the input slit. The input and output slits are disposed at 90 degrees from each other around a surface of revolution of the tube.
Care is required in introducing light into any integrating cylinder. For example, uniformity of the light across the output slit, efficiency of the integrating cylinder, and mechanical ease in using the integrating cylinder in a film scanner are some of the elements that must be considered. In this regard, U.S. Pat. No. 5,103,385 uses a baffle which trades some efficiency for mechanical ease, and U.S. Pat. Nos. 4,899,040 and 4,933,779 use integrating cylinders that trade some efficiency for uniformity of the output light and mechanical ease. However, none of the prior art integrating cylinder designs include the three considerations described above.
It is desirable to provide an integrating cavity for an film scanner which provides mechanical ease of use, an extremely uniform line of diffuse light at the output slit, and a maximum efficiency while reducing the complexity of a film gate of a film scanner.